Especially in case of shoes provided with a rubber sole it is extremely important to ensure an effective ventilation of the foot in order to avoid that an excessive perspiration causes the sweat to impregnate the fixed insole in contact with the skin of the foot and to produce annoying damages such as reddening of the skin, sores, etc., besides bad smell.
On the other hand many shoes with leather sole are not devoid of such a trouble.
In order to overcome such a problem a number of solutions have been brought forward, among which a recent one has been described in Italian Patent No. 1,232,798, available on the market with the name GEOX (registered trademark). Such a solution provides an osmotic membrane placed in the rubber sole and communicating with the inside of the shoe through holes in the fixed insole and with the outside through holes in the tread. As a result, the sole is made to transpire, though it stays impermeable to humidity. Although the membrane is protected by suitable layers of inert, transpiring material and it stands the mechanical stress due to the extension and torsions caused by the movement during walking, such a solution does not provide suitable guarantees of durability for the shoe as it requires strict maintenance conditions which cannot be easily kept up. One example is that the shoe must not be dried by heat sources so as not to damage the membrane.